Revert "Make artifact downloading more robust for flaky networks" (#13995)

* Revert "Change github readme links to be served by github (#13929)"

This reverts commit fd516d95.

* Revert " Rename SemanticsFlags to SemanticsFlag (#13994)"

This reverts commit 24e3f705.

* Revert "Make artifact downloading more robust for flaky networks (#13984)"

This reverts commit 4d37e03e.

packages/flutter_tools/lib/src/base/os.dart

@@ -47,14 +47,8 @@ abstract class OperatingSystemUtils {
 
   void unzip(File file, Directory targetDirectory);
 
-  /// Returns true if the ZIP is not corrupt.
-  bool verifyZip(File file);
-
   void unpack(File gzippedTarFile, Directory targetDirectory);
 
-  /// Returns true if the gzip is not corrupt (does not check tar).
-  bool verifyGzip(File gzippedFile);
-
   /// Returns a pretty name string for the current operating system.
   ///
   /// If available, the detailed version of the OS is included.
@@ -105,18 +99,12 @@ class _PosixUtils extends OperatingSystemUtils {
     runSync(<String>['unzip', '-o', '-q', file.path, '-d', targetDirectory.path]);
   }
 
-  @override
-  bool verifyZip(File zipFile) => exitsHappy(<String>['zip', '-T', zipFile.path]);
-
   // tar -xzf tarball -C dest
   @override
   void unpack(File gzippedTarFile, Directory targetDirectory) {
     runSync(<String>['tar', '-xzf', gzippedTarFile.path, '-C', targetDirectory.path]);
   }
 
-  @override
-  bool verifyGzip(File gzippedFile) => exitsHappy(<String>['gzip', '-t', gzippedFile.path]);
-
   @override
   File makePipe(String path) {
     runSync(<String>['mkfifo', path]);
@@ -190,18 +178,6 @@ class _WindowsUtils extends OperatingSystemUtils {
     _unpackArchive(archive, targetDirectory);
   }
 
-  @override
-  bool verifyZip(File zipFile) {
-    try {
-      new ZipDecoder().decodeBytes(zipFile.readAsBytesSync(), verify: true);
-    } on FileSystemException catch (_) {
-      return false;
-    } on ArchiveException catch (_) {
-      return false;
-    }
-    return true;
-  }
-
   @override
   void unpack(File gzippedTarFile, Directory targetDirectory) {
     final Archive archive = new TarDecoder().decodeBytes(
@@ -210,18 +186,6 @@ class _WindowsUtils extends OperatingSystemUtils {
     _unpackArchive(archive, targetDirectory);
   }
 
-  @override
-  bool verifyGzip(File gzipFile) {
-    try {
-      new GZipDecoder().decodeBytes(gzipFile.readAsBytesSync(), verify: true);
-    } on FileSystemException catch (_) {
-      return false;
-    } on ArchiveException catch (_) {
-      return false;
-    }
-    return true;
-  }
-
   void _unpackArchive(Archive archive, Directory targetDirectory) {
     for (ArchiveFile archiveFile in archive.files) {
       // The archive package doesn't correctly set isFile.

packages/flutter_tools/lib/src/cache.dart

@@ -162,9 +162,6 @@ class Cache {
     return dir;
   }
 
-  /// Return the top-level directory for artifact downloads.
-  Directory getDownloadDir() => getCacheDir('downloads');
-
   /// Return the top-level mutable directory in the cache; this is `bin/cache/artifacts`.
   Directory getCacheArtifacts() => getCacheDir('artifacts');
 
@@ -235,12 +232,6 @@ abstract class CachedArtifact {
   Directory get location => cache.getArtifactDirectory(name);
   String get version => cache.getVersionFor(name);
 
-  /// Keep track of the files we've downloaded for this execution so we
-  /// can delete them after completion.  We don't delete them right after
-  /// extraction in case [update] is interrupted, so we can restart without
-  /// starting from scratch.
-  final List<File> _downloadedFiles = <File>[];
-
   bool isUpToDate() {
     if (!location.existsSync())
       return false;
@@ -255,14 +246,6 @@ abstract class CachedArtifact {
     location.createSync(recursive: true);
     await updateInner();
     cache.setStampFor(name, version);
-    _removeDownloadedFiles();
-  }
-
-  /// Clear any zip/gzip files downloaded.
-  void _removeDownloadedFiles() {
-    for (File f in _downloadedFiles) {
-      f.deleteSync();
-    }
   }
 
   /// Hook method for extra checks for being up-to-date.
@@ -280,36 +263,6 @@ abstract class CachedArtifact {
   }
 
   Uri _toStorageUri(String path) => Uri.parse('$_storageBaseUrl/$path');
-
-  /// Download a zip archive from the given [url] and unzip it to [location].
-  Future<Null> _downloadZipArchive(Uri url, Directory location) {
-    return _withDownloadFile('${_flattenName(url)}.zip', (File tempFile) async {
-      if (!os.verifyZip(tempFile)) {
-        await _downloadFile(url, tempFile);
-      }
-      _ensureExists(location);
-      os.unzip(tempFile, location);
-    });
-  }
-
-  /// Download a gzipped tarball from the given [url] and unpack it to [location].
-  Future<Null> _downloadZippedTarball(Uri url, Directory location) {
-    return _withDownloadFile('${_flattenName(url)}.tgz', (File tempFile) async {
-      if (!os.verifyGzip(tempFile)) {
-        await _downloadFile(url, tempFile);
-      }
-      _ensureExists(location);
-      os.unpack(tempFile, location);
-    });
-  }
-
-  /// Create a temporary file and invoke [onTemporaryFile] with the file as
-  /// argument, then add the temporary file to the [_downloadedFiles].
-  Future<Null> _withDownloadFile(String name, Future<Null> onTemporaryFile(File file)) async {
-    final File tempFile = fs.file(fs.path.join(cache.getDownloadDir().path, name));
-    _downloadedFiles.add(tempFile);
-    await onTemporaryFile(tempFile);
-  }
 }
 
 bool _hasWarnedAboutStorageOverride = false;
@@ -493,32 +446,6 @@ class GradleWrapper extends CachedArtifact {
   }
 }
 
-// Many characters are problematic in filenames, especially on Windows.
-final Map<int, List<int>> _flattenNameSubstitutions = <int, List<int>>{
-  r'@'.codeUnitAt(0): '@@'.codeUnits,
-  r'/'.codeUnitAt(0): '@s@'.codeUnits,
-  r'\'.codeUnitAt(0): '@bs@'.codeUnits,
-  r':'.codeUnitAt(0): '@c@'.codeUnits,
-  r'%'.codeUnitAt(0): '@per@'.codeUnits,
-  r'*'.codeUnitAt(0): '@ast@'.codeUnits,
-  r'<'.codeUnitAt(0): '@lt@'.codeUnits,
-  r'>'.codeUnitAt(0): '@gt@'.codeUnits,
-  r'"'.codeUnitAt(0): '@q@'.codeUnits,
-  r'|'.codeUnitAt(0): '@pip@'.codeUnits,
-  r'?'.codeUnitAt(0): '@ques@'.codeUnits
-};
-
-/// Given a name containing slashes, colons, and backslashes, expand it into
-/// something that doesn't.
-String _flattenName(Uri url) {
-  final String urlName = url.toString();
-  final List<int> replacedCodeUnits = <int>[];
-  for (int codeUnit in urlName.codeUnits) {
-    replacedCodeUnits.addAll(_flattenNameSubstitutions[codeUnit] ?? <int>[codeUnit]);
-  }
-  return new String.fromCharCodes(replacedCodeUnits);
-}
-
 /// Download a file from the given [url] and write it to [location].
 Future<Null> _downloadFile(Uri url, File location) async {
   _ensureExists(location.parent);
@@ -526,6 +453,35 @@ Future<Null> _downloadFile(Uri url, File location) async {
   location.writeAsBytesSync(fileBytes, flush: true);
 }
 
+/// Download a zip archive from the given [url] and unzip it to [location].
+Future<Null> _downloadZipArchive(Uri url, Directory location) {
+  return _withTemporaryFile('download.zip', (File tempFile) async {
+    await _downloadFile(url, tempFile);
+    _ensureExists(location);
+    os.unzip(tempFile, location);
+  });
+}
+
+/// Download a gzipped tarball from the given [url] and unpack it to [location].
+Future<Null> _downloadZippedTarball(Uri url, Directory location) {
+  return _withTemporaryFile('download.tgz', (File tempFile) async {
+    await _downloadFile(url, tempFile);
+    _ensureExists(location);
+    os.unpack(tempFile, location);
+  });
+}
+
+/// Create a file with the given name in a new temporary directory, invoke
+/// [onTemporaryFile] with the file as argument, then delete the temporary
+/// directory.
+Future<Null> _withTemporaryFile(String name, Future<Null> onTemporaryFile(File file)) async {
+  final Directory tempDir = fs.systemTempDirectory.createTempSync();
+  final File tempFile = fs.file(fs.path.join(tempDir.path, name));
+  await onTemporaryFile(tempFile).whenComplete(() {
+    tempDir.delete(recursive: true);
+  });
+}
+
 /// Create the given [directory] and parents, as necessary.
 void _ensureExists(Directory directory) {
   if (!directory.existsSync())